This invention relates to position sensing devices and more particularly to a device for optically sensing the relative position of two or more movable devices.
Devices for determining the position of at least two objects movable relative to each other are in use in various fields of technology. For example, one application of such devices involves the sorting out from a number of objects those which possess identical properties and which are therefore provided with identical markers or flags. Devices in this category include index card files provided with hole-punched tabs in which the index cards are arranged in a package. By the use of a rod, those index cards whose tabs are in alignment with one another may be simultaneously removed. Another type of such well-known devices are what is referred to as "numerical locks" consisting of a set of numbered dials having a central hole and circumferentially spaced, peripheral notches. If all the notches of the set of dials are in alignment, a lug with a radial mandrel may be inserted in the aligned holes. Preadjusted drum-type counters operate on a similar principle. Also, well-known is a positioning and controlling device utilizing perforated tapes, with which a free-flowing medium, preferably a pressurized gas, is used as a flag sensor.
Devices having mechanical sensing of flags operate in a purely "static" manner, i.e., changes in position of the individual objects or elements (index cards, discs, etc.) remain undetected for a period of time and such changes can only be determined by experimental introduction of a test rod or the like or they are not of any practical use as long as the test rod is introduced. On the other hand, mechanisms employing a free-flowing medium operate "dynamically", that is, the individual elements can move freely towards each other so that a particular relative position of the elements is determined while "in motion". Nevertheless, to use such a free-flowing medium as for example, pressurized gas, the provision of a large number of auxiliary devices is required which makes such a system relatively stationary, requiring monitoring, and such a system is not only likely to malfunction but is expensive.
As a matter of fact, pre-set counters of the above mentioned type are commercially available and include optical elements formed by a pin diaphragm. However, only when the apertures of these pin diaphragms are in alignment, thus allowing the energy beam to pass through, is the desired position attained. In general, such devices require that the desired position be set at first, and thereafter the counter set at " 0". In this way, the desired position is marked by the zero positioning of the counter, and could at any time be located. The drawback of such a system is that it is first necessary to seek out the desired position in order to be able to mark it. In the case of magnetic equipment, it is often necessary from the outset to provide specific well-known counters so that a specific musical transmission or the like begins on a specific tape. In another well-known design, it has been suggested that the apertures of the pin diaphragms be put at optional points corresponding to a specific position, for example. Here again, the disadvantage is that once the apertures have been made, they are not readily interchangeable, so that when used on magnetic tape equipment, a specific position can certainly be detected in such a mechanical memory device but not different positions, such as would be required for different magnetic tapes.
In accordance with the invention, a device of the above-mentioned type has been provided which does not have the disadvantages of such previously known devices. According to the invention, this is accomplished by providing optical elements such as deflecting prisms associated in adjustable pairs and supported on the objects such as in a counter particularly for deflecting an energy beam whereby a deflecting element of an object is associated with another deflecting element such as the element of pre-set disc to form a pair of such elements in such a way that the energy beam is directed to a receiver only when the adjusted position of the disc and the position of the object coincide. By so doing, any position may be pre-set or determined without any concern with the zero position or some other predetermined position. With the invention, visible or invisible light, laser beams or even collected high frequency beams may be employed to serve as an electromagnetic beam.